In recent years, there has been an increasing demand for improvement in power conversion efficiency in the power electronics industry, in order to reduce the amount of greenhouse gas emission to prevent global warming.
Switching devices such as power metal-oxide-semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs) which include silicon as material have been used for power electronic circuits.
Research has been conducted on achieving switching devices to be practically utilized which include group III nitride semiconductors that cause less loss, instead of switching devices which include silicon.
However, a phenomenon called current collapse easily occurs in a switching device which includes a group III nitride semiconductor as material.
A current collapse phenomenon is a temporal change in the current at the time of switching. For example, a portion in which crystal on the surface or inside of a semiconductor layer has defect and a portion damaged due to a processing process serve as traps for collecting electric charge. Electric charge is collected by such traps or electric charge is released from the traps, thereby causing a temporal change in a current at the time of switching. The temporal change in a current is a current collapse phenomenon.